Steroids of a common oral contracepitve, 'Norinyl' are composed of norethindrone (progestin) and mestranol (estrogen), and will be fed either singly or in combination to ovariectomized guinea pigs. With such an experimental design, this study will identify which of these steroids, or whether the combined components, are responsible for the reduced tissue ascorbic acid concentrations established in women and guinea pigs. One of the major objectives of this project is to elucidate the mechanism(s) responsible for the alteration of vitamin C metabolism. The reduction of tissue ascorbic acid levels may be caused by a shift of ascorbic acid from one pool to another, or due to an increase in degradation rate. The rate of intestinal absorption, pulmonary elimination and urinary and fecal excretion of ascorbic acid will be examined. The overall catabolic rates of ascorbic acid will be studied by measuring the production rates of 14C-labeled; respiratory CO2, urinary ascorbic acid, dehydroascorbic acid, 2, 3-diketogulonic acid and oxalic acid after intramuscular injections of ascorbic acid - U - 14C in guinea pigs. The pool size, half life, turnover rate and time will be studied in several tissues and organs as well as in the whole body of guinea pigs by using the isotope dilution technique. Furthermore, in vitro studies will be carried out to measure the degradation rate of ascorbic acid by plasma ceruloplasmin ascorbic acid oxidase and copper, and the catabolism of 2, 3-diketogulonic acid by liver decarboxylase. The in vitro reaction will be monitored by measuring the quantities of products formed or the remaining substrate.